Understanding Fusaka: Ethereum's Upcoming Upgrade

On December 3, 2025, Ethereum will launch the Fusaka upgrade, marking its second significant hard fork of the year after Pectra in May. Fusaka aims to alleviate the constraints on rollups that currently handle much of Ethereum's transactions and fee revenue. Its standout feature, PeerDAS (Peer Data Availability Sampling), will enable validators to verify rollup data more efficiently, enhancing overall data throughput. This article will explore what changes Fusaka introduces, its context within Ethereum's roadmap, and its potential implications for users and the ecosystem.

Key Takeaways

Fusaka will be activated on December 3, 2025, as Ethereum's major update.
The upgrade features PeerDAS, which improves data verification efficiency for rollups.
Fusaka introduces innovations like blob parameter-only forks to enhance scalability gradually.
The upgrade will facilitate a higher transaction throughput while maintaining network security.
Future developments, including the Glamsterdam upgrade in 2026, promise further improvements.

What is Fusaka?

On December 3, 2025, Ethereum aims to activate the Fusaka upgrade on its mainnet. This upgrade is the second major hard fork of the year, following the Pectra upgrade in May. Currently, rollups handle the majority of transactions and fee revenue on Ethereum, but they are limited by how much data they can post back to the layer 1 and the associated costs. Fusaka seeks to address these limitations.

One of the upgrade's key features, PeerDAS (Peer Data Availability Sampling), allows validators to verify rollup blob data without requiring them to download everything. This significantly reduces bandwidth and storage needs while paving the way for much higher data throughput. Additionally, Fusaka introduces blob-only parameter (BPO) forks, updates gas and block size limitations, and enhances history expiry measures. Together, these changes prepare the Ethereum chain for ongoing capacity increases.

Did you know? Fusaka's name is a fusion of two internal upgrade code names, Osaka (Execution Layer) and Fulu (Consensus Layer).

The Roadmap: From Merge to Fusaka

To understand Fusaka's place within Ethereum's development, it is helpful to look at the preceding upgrades:

The Merge (2022) transitioned Ethereum from a proof-of-work to a proof-of-stake model, reducing energy consumption by about 99.9%.
Shapella (2023) allowed for the withdrawal of staked Ether, making staking liquid and attracting more validators.
Dencun (March 2024) introduced Ethereum Improvement Proposal (EIP) 4844 "blobs," which offered a cheaper, temporary data solution for rollups, referred to as protodanksharding.
Pectra (May 2025) brought in EIP-7702 account abstraction features and revised staking parameters, such as establishing a 2,048-ETH validator cap.

These upgrades align with Vitalik Buterin's roadmap: Merge, Surge, Verge, Purge, and Splurge. Fusaka is unique in that it addresses multiple aspects of this roadmap simultaneously, expanding data capacity for rollups as part of the Surge while incorporating elements of history expiry and lighter synchronization relevant to the Verge and Purge.

Technology

Enhancements: PeerDAS, Blobs, and Bigger Blocks

The core change implemented by Fusaka is through EIP-7594, known as PeerDAS. Instead of requiring every full node to download complete blobs of rollup data, PeerDAS breaks these blobs into smaller segments. This allows validators to sample random parts of these blobs, making it possible to verify full data availability without downloading everything at once.

This approach minimizes the bandwidth and storage needed per node, setting the stage for the potential to increase blob capacities significantly over time. To facilitate more manageable growth, EIP-7892 introduces Blob Parameter Only (BPO) forks, which are smaller hard forks focused solely on a few blob-related parameters, enabling Ethereum to adjust blob capacity in smaller increments as demand rises.

From an execution perspective, Fusaka modifies gas and block size parameters:

The effective block gas target will increase from the current 45 million gas limit to much higher ceilings. EIP-7825 will cap the gas used per single transaction, while EIP-7934 introduces a 10 MB Recursive Length Prefix block size limit to mitigate denial-of-service risks.
EIPs 7823 and 7883 will re-evaluate and limit the MODEXP precompile, ensuring that heavy cryptographic calls do not stall an entire block.

Overall, Fusaka equips Ethereum to handle more rollup data and complex transactions while incorporating safeguards that ensure blocks remain verifiable for regular nodes.

Did you know? Blobs are temporary data packets posted by rollups to Ethereum, offering a cost-effective solution that is automatically pruned after approximately 18 days to prevent bloating on the chain.

User Experience, Security, and Developer Tools

The Fusaka upgrade goes beyond just enhancing capacity; it also includes several EIPs that improve user experience, security, and developer tools. For example, EIP-7917 introduces a deterministic proposer lookahead, making future proposer schedules fully predictable and accessible on the blockchain through the beacon root. This is crucial for rollups and pre-confirmation schemes that require knowledge of which validator will propose a block, ensuring rapid and reliable soft finality.

In terms of user experience, EIP-7951 adds support for the secp256r1 signature, allowing Ethereum to easily incorporate biometric authentication into wallets. This aligns better with mainstream fintech services that rely on device biometrics rather than seed phrases for security.

Developer enhancements include EIP-7939, which facilitates the computation of leading zeros in a 256-bit word, streamlining bit-level math and certain zero-knowledge proof circuits. Furthermore, EIP-7642 advances Ethereum’s history expiry efforts, allowing clients to eliminate older data while providing an efficient way to manage node synchronization.

Impacts: Who Benefits from Fusaka?

For layer-2 (L2) ecosystems, the benefits of Fusaka are clear. The combination of PeerDAS and BPO forks should lead to a considerable reduction in L2 data costs over time—potentially by 40%-60%. This decrease in costs opens up more opportunities for experimentation and competition among rollups, especially in areas such as decentralized finance (DeFi), gaming, and social applications.

Node operators and validators will experience mixed effects. While sampling and history expiry ease data storage and download requirements, the increased blob count from BPO forks may require better-resourced validators to manage more upload bandwidth. This could lead to a gradual shift towards larger operators unless client implementations provide sufficient guidance.

For institutions and staking providers, Fusaka is perceived as a strategic advancement rather than a one-off enhancement. With more predictable data flow and well-managed gas limits, large-scale validator operations become easier to plan.

For ETH holders, the changes indicate that Ethereum's base layer is evolving into a high-capacity engine facilitating L2 transactions. Adjustments to minimum fees and blob pricing could influence market dynamics and validator rewards based on user demand. However, increased complexity and a shift towards monetization may raise concerns if everyday users do not experience clear improvements.

Did you know? The activation slot for Fusaka was set during the final coordination call, slated for slot 13,164,544 around 21:49 UTC on December 3, 2025.

Looking Ahead: Glamsterdam and Beyond

The next significant upgrade, Glamsterdam, is anticipated for 2026 and will introduce crucial features such as enshrined proposer builder separation (ePBS) and block-level access lists (BALs). ePBS aims to strengthen the maximal extractable value (MEV) supply process by separating block building and proposing at the protocol level. Meanwhile, BALs will enhance execution efficiency and manage state access as blob capacity increases.

Both the PeerDAS and BPO forks will advance the Surge's objectives, while history expiry and P2P adjustments align with the Verge and Purge upgrades. User-focused enhancements like proposer lookahead and P-256 support will make soft confirmations and passkey wallets scalable.

If Ethereum successfully implements these upgrades, Fusaka may be seen not just as a single event, but as a defining moment in the evolution of Ethereum’s roadmap, leading towards a modular stack capable of 100,000 transactions per second (TPS) without compromising the decentralization that is integral to its value.